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Linux Kernel Power Management Targeting Memory

04-10-2013, 01:10 AM

Phoronix: Linux Kernel Power Management Targeting Memory

One of the areas of hardware power management that can yield a surprising amount of power-savings but is often overlooked comes down to the system memory. Fortunately, new Linux kernel patches continue to be written for improving the Linux kernel RAM power management...

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ARM draws little power, so 6% power save show up as significant.
However, on ARM systems such as smartphones and tablets, what draw the most power is the screen.

On x86 processors, the power saved would be negligible.

I think it depends on how this works. For example, I'm pretty sure you can't (effectively) tell a particular column in a single memory chip to operate in a lower-power state while the rest of the IC is at full power. However, you might be able to lower the power consumption of an entire memory chip in a DIMM, but perhaps the entirety of DIMMs are what get affected. Anyways, nearly all ARM SoCs involve a single IC for RAM, and if I'm right about individual columns/rows being unable to change their power state, then ARM systems will get a 0% benefit from this.

I feel like the people who would benefit from this most are those who have 4+ DIMMs and are either overclockers or use ECC memory. Considering the overkill amount of RAM people buy these days, entire RAM modules could be completely ignored by the OS, which would save a decent amount of power.

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However, on ARM systems such as smartphones and tablets, what draw the most power is the screen.

While that is true, when you look at good reviews of devices, you see significant differences in phones/tablets with similar screen sizes.
Apple sports a pretty impressive power management system (across all their devices) that shows up even when correcting for screen power draw. So, looking at other parts of the system can make a huge difference (more than this 6%, even).
Look at the latest big Anandtech review of the HTC One. The iphone 5 tops, or near the top, for every battery test they have the least amount of control over (telephony being a part they just have to accept from whoever makes their telephony chips).

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RAM drives are nice, I even created an automated script to generate them, but I have yet to find a real practical use for them aside from live CDs. If there was a way to attach the RAM drive to at least 1 SATA port (but preferably more so I can do RAID 0) then RAM drives would be fantastic because then I could store an OS on them and boot from another computer. Imagine that though - a 4x RAID 0 RAM drive on SATA 3 - that's going to offer some performance you just simply can't beat.

I'm really surprised someone hasn't created a SATA "bridge" like this yet. Or, a RAM drive that works this way. I'm sure it'd be wildly popular. The only true RAM drives that were made were SATAII and limited to like... 8GB. Modern SSDs are better, and cheaper.